1. Field of the Invention
The invention relates to a novel multistable electron beam addressed electroluminescent storage display panel. More particularly, it relates to a storage display panel which can be activated by direct electron beam radiation in the presence of an A.C. field via direct electron beam activation of an electroluminescent film or by electron beam induced light activation of said electroluminescent film.
2. Prior Art
For computer display often large information content is involved, the refresh cathode ray tubes require a large memory which is costly. For instance, to display a 8000 character text, a storage memory of 5 .times. 10.sup.5 bits is required. Thus there is a need for a memory display device which contains internal memory. None of the present day CRT devices except complex flood gun structures meet the memory requirements aforementioned.
There have been several attempts to fabricate storage CRT's to meet the above-stated requirements. Until the present invention none of the CRT's presently in use approached these requirements.
What is perhaps the most recent advance in electroluminescent bistable storage display devices is described in U.S. Pat. No. 3,796,909 to Chang et al. This device is innovative in that it describes a storage display concept wherein an A.C. field-sensitive material is used as the display medium. A secondary electron emitting layer is used for storage medium. An image is displayed by electroluminescence rather than from cathodoluminescence as in some earlier prior art devices. In this device a charge pattern is written on an electroluminescent target by a "writing" electron beam. This "written charge pattern" electron beam is maintained by a "flood" electron beam via a secondary electron emission process to establish a voltage pattern corresponding to the written charge pattern. An A.C. potential is applied to the electroluminescent target via a transparent electrode on the face-plate. The A.C. potential produces an A.C. field in the electroluminescent target only in the region where its inner surface is maintained at a fixed collector potential by the flood electron beam. Thus, the electroluminescent image is generated according to a stored charged pattern. This has the advantage of improved brightness, because the electroluminescent target is not dependent on the flood beam potential and can be independently adjusted by varying the A.C. voltage and frequency as the flood beam is maintaining the bistability. The major drawbacks of this device are that much of the flood beam energy is dissipated from the face-plate as heat. Moreover, the device exhibits bistability only, which limits usefulness of display. In many display applications such as business graphing matrix displays and text editing displays, it is desirable to have multilevel intensities (brightness) so that images of gray scale and intensity modulation (either for information coding purpose or attention getting purpose), can be displayed.
A more recent discovery, the A.C. field sensitive electroluminescent displays has been made by P. Inoguchi et al, Digest 1974 Society for Information Display International Symposium, Los Angeles, 1974 p. 84. More recent studies of this recent discovery have been made by Yamauchi et al., IEEE, 1974 IEDM Digest, and C. Suzaki et al., Digest, 1976, Society for Information Display International Symposium, Los Angeles 1976 p. 50. P. Inoguchi et al., discovered that an electroluminescent target can be biased with a sustaining A.C. voltage below its normal threshold voltage and can be subsequently activated or switched to an on state by applying a light pulse. Because of the hysteresis loop characteristics of this type electroluminescent device there is exhibited multistability or memory. The light pulses are effected by a high pressure mercury lamp.
What has been discovered in the present application is that a CRT can be fabricated which has memory or gray scale functions. It has been further discovered that the electroluminescent target can be directly activated by electron beam, or alternately, by light induced by electron beam radiation. Since the mechanism of both the electron beam switching and light switching are not known to workers in the field of electroluminescence and displays, the discovery of electron beam switching, particularly, in a serial manner, is not like exposing the entire device to an optical image simultaneously to achieve optical switching, nor like exposing the entire device to flood beam electrons which are required to maintain a fixed voltage over the high energy beam written pattern serving as an AC voltage reference.